Well whatever he did isn't visible now from the interior. This was like 5 years ago, so maybe my memory is failing me, but I recall some sort of rivet in the material. I am thinking it was to expand the material and wedge it in the track?
Any old time convertible top guy should know. He wasn't phased by this,so probably something they are used to.
Are you planning on doing this yourself? If yes, then you are more daring then I. He had a hell of a time installing my top making it fit well with no wrinkles in the C-pillar. Not something I wanted to tackle.